<accordion>
  <accordion-group heading="Static Header, initially expanded"
                   [panelClass]="customClass"
                   [isOpen]="isFirstOpen">
    This content is straight in the template.
  </accordion-group>
  <accordion-group heading="Content 1">
    <p>accordion 1</p>
  </accordion-group>
  <accordion-group heading="Content 2" panelClass="customClass">
    <p>accordion 2</p>
  </accordion-group>
</accordion>
